The present invention relates to pintle-type valves; more particularly, to such valves for variably regulating the flow of fluids and especially gases; and most particularly, to a multiple-stage pintle valve having a greatly expanded range of fluid metering, wherein a low-flow valve is disposed within the valve head of a high-flow valve, the two valves being actuated sequentially by a common pintle shaft and actuator.
Pintle-type valves are used for a wide variety of on/off and metering functions. In general, pintle valves are not well-suited to metering, since flow across the valve seat as a function of pintle and head travel typically is quite non-linear. Many pintle valves go from fully closed to substantially fully open with a relatively short stroke of the actuator, thus making difficult the precise metering of fluid at intermediate degrees of openness. Such valves are said to have a narrow dynamic range. For low total flow applications, relatively small valves typically are used, and for larger total flow applications, larger valves are used. However, a serious problem arises in applications wherein a given pintle valve is required to meter fluid over a wide range of flows.
It is well known in the automotive art to provide a variable valve connecting the exhaust manifold with the intake manifold of an internal combustion engine to permit selective and controlled recirculation of a portion of an engine""s exhaust gas into the fuel intake stream. Such recirculation is beneficial for reducing the burn temperature of the fuel mix in the engine to reduce formation of nitrogen and sulfur oxides which are significant components of smog. Such a valve is known in the art as an exhaust gas recirculation (EGR) valve.
Typically, an EGR valve is a pintle-type valve having a valve body enclosing a chamber disposed between a first port in the exhaust manifold and a second port in the intake manifold; a valve seat dividing the chamber between the two ports; a valve head fitted to mate with the valve seat; a valve stem or pintle extending from the valve head through a bore in a sidewall of the valve body; and a solenoid actuator mounted on the exterior of the valve body and operationally connected to the outer end of the valve stem. The stroke of the solenoid is regulated as by a computer in response to the composition of the intake and exhaust streams to vary the axial position of the valve pintle and valve head with respect to the valve seat to provide a desired flow volume of exhaust gas through the valve.
Because of the dynamic range limitations of known pintle-type valves, a wide range of EGR valve sizes is presently required for optimum metering on a wide range of engine sizes. Large engines require large EGR valves, and smaller engines require smaller EGR valves. A large EGR valve on a small engine cannot be controlled with the degree of flow resolution required. If an EGR valve is too small for an engine, then fuel economy and emissions quality can be compromised; if sized too large, then controllability, durability, and performance can be compromised.
What is needed is a means for extending the dynamic range of a pintle valve so that a single valve can be used over a wide range of flow requirements, thus reducing manufacturing and replacement part complexity and cost.
It is the primary object of the invention to provide an improved pintle valve which extends the precise controllable range of a single valve over a broad range of flow requirements.
It is a further object of the invention to save cost and complexity in manufacturing and inventorying a wide variety of sizes of pintle valves.
The invention is directed to a pintle valve comprising a plurality of stages. Each stage comprises a valve seat and head capable of regulating flow through the valve over its own dynamic range. The valve head of a higher-flow stage includes the valve seat for the next-lower flow stage. The heads and seats for the multiple stages are nested concentrically, the progressively lower-flow stages having progressively smaller diameters. All valve heads except the lowest-flow head have axial and radial bores permitting flow therethrough so that flow may be regulated first by actuating the lowest-flow stage, then by actuating successively higher flow stages. A single pintle shaft connected to a solenoid actuator is adapted to engage each of the valve heads sequentially as the actuator progresses, beginning with the lowest-flow head, thereby extending incrementally the dynamic range of the valve as each head is successively engaged.